I’ve been building an NES emulator in C++ for the past few months. It’s not quite finished yet, but I wanted to share some details about the project, the tech stack, and my progress so far.
Quick disclaimer! I’m actually working on two NES emulators: one as a personal project and another as part of a school group. I’m a bit ahead of the group, so when I say “I,” I’m referring to my personal project and insights, not dismissing the team’s work!
The Project
My emulator is about halfway done. The CPU is functional and passes many common tests, and the PPU is nearly complete.
Here’s what it looks like:
It’s blank! In computer graphics, things either work perfectly or not at all; there’s rarely an in-between. Despite the empty screen, reaching this stage required significant effort. Now, I’ll discuss the technologies I’ve used.
The Tech Stack
I chose C++ because I wanted to get better at it. It was tempting to jump in right away, but one lesson I’ve learned from past projects is that a solid setup saves trouble later. So, I spent a few days setting up an environment that would serve me well.
CMake
I went with CMake for the build system because it supports multiple platforms. While make might seem simpler, it quickly becomes cumbersome as a project grows. I wanted to avoid reworking my build system later, so I set up CMake from the start.
Google Test
Google Test was my first dependency. I started with a basic test to confirm everything was working. The NES has a lot of community-made test ROMs, which I integrated to help with CPU development.
SDL2
For windowing and graphics, I chose SDL2, mostly because there wasn’t a real alternative. I’m familiar with OpenGL, but setting it up for cross-platform use wasn’t something I wanted to deal with. SDL provides an all-in-one solution for video, audio, and input, so there was no reason to reinvent the wheel.
Clang-format and Clang-tidy
These tools help with formatting and static analysis. Clang-Format enforces style rules, while Clang-Tidy catches potential issues. For example, my .clang-format file follows Linux-style braces:
And my .clang-tidy file enforces camelBack variable names:
I also set these up in the group project, with a GitHub action to run lint checks on every PR. It’s helped keep the codebase consistent.
That said, clang-tidy isn’t perfect. It runs on the entire codebase and all linked headers, which can be slow. But for this project, the benefits outweigh the downsides.
Cross-platform Tools
Since I need to test builds on macOS, Windows, and Linux, I’ve been using a few different tools. Mac is my main OS, so that’s covered. For Windows, I load a Windows 10 VM with VMWare Fusion and build with Visual Studio. For Linux, I use Docker with an Ubuntu image, which also lets me run tools like Valgrind that aren’t available on macOS.
Debugging
For debugging, I mostly use CLion, even though my usual editor is Neovim. CLion’s step debugger has been invaluable. I also use the Mesen emulator and its debugging tools to cross-check how things should behave on a proper emulator.
Upcoming Additions to the Stack
I’m planning to add vcpkg to the project. I spent a lot of time getting SDL2 working across all three platforms, and I’d rather not go through that again. So why bother now, if it’s already working? Because I’m planning to add imgui for UI soon, which will come with its own cross-platform problems. vcpkg can handle platform-specific installation, which will leave me free to focus on the fun stuff!
Setting up libraries isn’t a big deal when it’s just my machine, but I try to keep setup overhead low for the team project as well. It’s a balance between what’s easiest for me and what’s easiest for everyone.
Conclusion
Looking back, this stack has worked well, and I’ll probably use a similar setup for future projects. CMake had a learning curve, but I’m getting more comfortable with it. One tool I’d like to explore next is Ninja. Ninja is a build system by Google that’s supposed to be much faster than make and supports parallel builds. Combined with CMake and vcpkg, it might finally make C++ dependency management a little more bearable.
As for project progress, I’m currently stuck debugging the PPU. I plan to add imgui and build some visual debugging tools to help figure out what’s going wrong.
That’s all for now! Thanks for reading!